Dual loss of regulator of G protein signaling 2 and 5 exacerbates ventricular myocyte arrhythmias and disrupts the fine-tuning of Gi/o signaling.

ABSTRACT

AIMS: Cardiac contractility, essential to maintaining proper cardiac output and circulation, is regulated by G protein-coupled receptor (GPCR) signaling. Previously, the absence of regulator of G protein signaling (RGS) 2 and 5, separately, was shown to cause G protein dysregulation, contributing to modest blood pressure elevation and exaggerated cardiac hypertrophic response to pressure-overload. Whether RGS2 and 5 redundantly control G protein signaling to maintain cardiovascular homeostasis is unknown. Here we examined how the dual absence of RGS2 and 5 (Rgs2/5 dbKO) affects blood pressure and cardiac structure and function. METHODS AND RESULTS: We found that Rgs2/5 dbKO mice showed left ventricular dilatation at baseline by echocardiography. Cardiac contractile response to dobutamine stress test was sex-dependently reduced in male Rgs2/5 dbKO relative to WT mice. When subjected to surgery-induced stress, male Rgs2/5 dbKO mice had 75% mortality within 72-96 h after surgery, accompanied by elevated baseline blood pressure and decreased cardiac contractile function. At the cellular level, cardiomyocytes (CM) from Rgs2/5 dbKO mice showed augmented Ca2+ transients and increased incidence of arrhythmia without augmented contractile response to electrical field stimulation (EFS) and activation of ß-adrenergic receptors (ßAR) with isoproterenol. Dual loss of Rgs2 and 5 suppressed forskolin-induced cAMP production, which was restored by Gi/o inactivation with pertussis toxin that also reduced arrhythmogenesis during EFS or ßAR stimulation. Cardiomyocyte NCX and PMCA mRNA expression was unaffected in Rgs2/5 dbKO male mice. However, there was an exaggerated elevation of EFS-induced cytoplasmic Ca2+ in the presence of SERCA blockade with thapsigargin. CONCLUSIONS: We conclude that RGS2 and 5 promote normal ventricular rhythm by coordinating their regulatory activity towards Gi/o signaling and facilitating cardiomyocyte calcium handling.